BOSTON — Investigators believe that two brothers suspected in the Boston Marathon bombing were likely planning other attacks based on the cache of weapons uncovered, the city’s police commissioner said Sunday.

As Boston-area residents came together in prayer and reflection after a tumultuous week, the lone surviving suspect in the bombing lay hospitalized under heavy guard apparently in no shape for interrogation.

What 19-year-old Dzhokhar Tsarnaev will say and when are unclear. He remained in serious condition two days after being pulled bloody and wounded from a tarp-covered boat in a Watertown backyard. The capture came at the end of a tense Friday that began with his 26-year-old brother, Tamerlan, dying in a gun battle with police.

There was no immediate word on when Tsarnaev might be charged and what those charges would be. The twin bombings killed three people and wounded more than 180.

The most serious charge available to federal prosecutors would be the use of a weapon of mass destruction to kill people, which carries a possible death sentence. Massachusetts does not have the death penalty.

Boston Police Commissioner Ed Davis told CBS’ “Face the Nation” that authorities found an arsenal of homemade explosives after Friday’s gun battle between police and the two suspects.

“We have reason to believe, based upon the evidence that was found at that scene — the explosions, the explosive ordnance that was unexploded and the firepower that they had — that they were going to attack other individuals,” Davis said. “That’s my belief at this point.”

The scene of the gun battle was loaded with unexploded bombs, and authorities had to alert arriving officers to them and clear the scene, Davis said. One improvised explosive device was found in the Mercedes the brothers are accused of carjacking, he said.

“This was as dangerous as it gets in urban policing,” Davis said.

U.S. officials said the elite interrogation team would question Tsarnaev, a Massachusetts college student, without reading him his Miranda rights, which guarantees the right to remain silent and the right to an attorney. Such an exception is allowed on a limited basis when the public may be in immediate danger, such as instances in which bombs are planted and ready to go off.

American Civil Liberties Union Executive Director Anthony Romero said the legal exception applies only when there is a continued threat to public safety and is “not an open-ended exception” to the Miranda rule.

The federal public defender’s office in Massachusetts said it has agreed to represent Tsarnaev once he is charged. Miriam Conrad, public defender for Massachusetts, said he should have a lawyer appointed as soon as possible because there are “serious issues regarding possible interrogation.”

But Republican Rep. Mike Rogers told NBC’s “Meet the Press” that he’s not worried that the government has decided against reading the suspect his rights. Rogers said FBI agents need to know whether there are other bombs more than they need to use in court what the suspect might tell them.

Rogers, a former FBI agent, said there is so much evidence against the suspect that a conviction should be easy.

Massachusetts Gov. Deval Patrick said Sunday that surveillance video from Monday’s Boston Marathon attack shows Dzhokhar Tsarnaev dropping his backpack and calmly walking away from it before the bomb inside it exploded.

“It does seem to be pretty clear that this suspect took the backpack off, put it down, did not react when the first explosion went off and then moved away from the backpack in time for the second explosion,” Patrick told NBC television. “It’s pretty clear about his involvement and pretty chilling, frankly.”

He added, however, that he hasn’t viewed all the tapes but had been briefed by law enforcement about them.

President Barack Obama said there are many unanswered questions about the bombing, including whether the Tsarnaev brothers - ethnic Chechens from southern Russia who had been in the U.S. for about a decade and lived in the Boston area - had help from others. The president urged people not to rush judgment about their motivations.

Speaking on “Face the Nation,” Patrick said that he has no idea what motivated the suspects. The governor said it’s hard to imagine why someone would deliberately harm “innocent men, women and children in the way that these two fellows did.”

Patrick also said law enforcers believe the immediate threat ended when police killed one suspect and captured the other.

Patrick said Saturday afternoon that Dzhokhar Tsarnaev was in serious but stable condition and was probably unable to communicate. Tsarnaev was at Boston’s Beth Israel Deaconess Medical Center, where 11 victims of the bombing were still being treated.

On Sunday, family and friends attended a wake at a funeral home in Medford, Massachusetts, for Krystle Campbell, a 29-year-old restaurant worker, who was one one of the three people killed in the marathon bombing. A private funeral is scheduled for Monday.

Eight-year-old Martin Richard of Boston’s Dorchester neighbourhood and 23-year-old Lu Lingzi, a Boston University graduate student from China, also died in the attacks. BU is holding a memorial service for Lu on Monday.

On Sunday, a Boston synagogue opened its doors to worshippers from Trinity Church, which sits in the shadow of the Marathon finish line and remains closed. An interfaith service will also be held Sunday near the finish line where people set up a make-shift memorial as police cleared away debris from the bombing. The Rev. Nancy Taylor of the Old South Church said worshippers will be showing solidarity with the bombing victims.

Cardinal Sean O’Malley was offering a Mass to pray for those killed and injured in the attack and manhunt for the suspects. The service will also honour police, firefighters, emergency medical technicians and doctors who saved lives.

The all-day manhunt Friday brought the Boston area to a near standstill and put people on edge across the metropolitan area.

The break came around nightfall when a homeowner in Watertown saw blood on his boat, pulled back the tarp and saw a bloody Dzhokhar Tsarnaev hiding inside, police said. After an exchange of gunfire, he was seized and taken away in an ambulance.

Raucous celebrations erupted in and around Boston, with chants of “USA! USA!” Residents flooded the streets in relief four days after the two pressure-cooker bombs packed with nails and other shrapnel went off.

During the long night of violence leading up to the capture, the Tsarnaev brothers killed a Massachusetts Institute of Technology police officer, severely wounded another lawman and took part in a furious shootout and car chase in which they hurled homemade explosives at police, authorities said.

Watertown Police Chief Edward Deveau said one of the explosives was the same type used during Monday’s Boston Marathon attack, and authorities later recovered a pressure cooker lid that had embedded in a car down the street. He said the suspects also tossed two grenades before Tamerlan Tsarnaev ran out of ammunition and police tackled him.

But while handcuffing him, officers had to dive out of the way as Dzhokhar drove the carjacked Mercedes at them, Deveau said. The sport utility vehicle dragged Tamerlan’s body down the block, he said. Police initially tracked the escaped suspect by a blood trail he left behind a house after he abandoned the Mercedes, negotiating his surrender hours later.

The federal Bureau of Alcohol, Tobacco, Firearms and Explosives is tracing the weapons to try to determine how they were obtained by the suspects.

Chechnya, where the Tsarnaev family has roots, has been the scene of two wars between Russian forces and separatists since 1994. That spawned an Islamic insurgency that has carried out deadly bombings in Russia and the region, although not in the West.

Investigators have not offered a motive for the Boston attack. But in interviews with officials and those who knew the Tsarnaevs, a picture has emerged of the older one as someone embittered toward the U.S., increasingly vehement in his Muslim faith and influential over his younger brother.

The Russian FSB intelligence service told the FBI in 2011 about information that Tamerlan Tsarnaev was a follower of radical Islam, two law enforcement officials said Saturday.

According to an FBI news release, a foreign government said that Tamerlan Tsarnaev appeared to be a strong believer and that he had changed drastically since 2010 as he prepared to leave the U.S. for travel to a region in Russia to join unspecified underground groups.

The FBI did not name the foreign government, but the two officials said it was Russia. The officials spoke on condition of anonymity because they were not authorized to talk about the matter publicly.

The FBI said that in response, its agents interviewed Tamerlan Tsarnaev and relatives, and did not find any domestic or foreign terrorism activity. The bureau said it looked into such things as his telephone and online activity, his travels and his associations with others.

An uncle of the Tsarnaev brothers said he had a falling-out with Tamerlan over the man’s increased commitment to Islam.

Ruslan Tsarni from Maryland said Tamerlan told him in a 2009 phone conversation that he had chosen “God’s business” over work or school. Tsarni said he then contacted a family friend who told him Tsarnaev had been influenced by a recent convert to Islam.

Tsarni said his relationship with his nephew basically ended after that call.

As for Dzhokhar Tsarnaev, “he’s been absolutely wasted by his older brother. I mean, he used him. He used him for whatever he’s done,” Tsarni said.

Albrecht Ammon, a downstairs-apartment neighbour of Tamerlan Tsarnaev in Cambridge, said in an interview that the older brother had strong political views about the United States. Ammon quoted Tsarnaev as saying that the U.S. uses the Bible as “an excuse for invading other countries.”

Tamerlan Tsarnaev studied accounting as a part-time student at Bunker Hill Community College in Boston for three semesters from 2006 to 2008, the school said. He was married with a young daughter.

Dzhokhar Tsarnaev was a student at the University of Massachusetts-Dartmouth. The college was evacuated Friday, but officials said residence and dining halls will reopen Sunday.

As of Saturday, more than 50 victims of the bombing remained hospitalized, three in critical condition.

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